The incorporation of fillers, for example, during the production of articles made from foams, particularly those made from polyurethane foams, allows specific qualities to be imparted to the finished product, and/or allows waste materials to be utilized and/or allows the material costs to be reduced. Examples of conventional fillers include, cement, lime or chalk, barium sulfate, organic fibers, inorganic fibers, and particularly short glass fibers and ground glass fibers, as well as powdered foam which has been produced from crushed foam scraps.
Piston cylinder units utilizing the positive displacement principle, wherein reactants are metered into the mixing chamber, or circulated, are already known. These apparatus operate in high pressure ranges, i.e. at injection pressures above about 20 bars. These high pressure ranges are eminently suitable and even essential when introducing large quantities of reactants, to be mixed, into the cavity of a mold within a short period. It must be applied, when fast reacting components are being used. The processing of filler-containing reactants with these previously known piston cylinder units gives rise to difficulties because the entire circulatory system has to be produced from wear-resistant material. It is doubtful whether the sometimes quite complicated control elements used in the mixer heads, for example, control pistons with return grooves, can be produced economically, from such materials, to conform to the tolerances necessary.
Methods are also known which operate in the so-called low pressure range, wherein the filler is introduced in the dry state, together with the reaction mixture, into a stirrer chamber where they are mixed together. However, it is only possible to apply this method with component systems that react slowly.